Steps towards [(C5Me5)TcO3]:: Novel synthesis of [(C5Me5)Tc(CO)3] from [{Tc(μ3-OH)(CO)3}4] and oxidation of [(C5Me5)M(CO)3] (M = Tc, Re) with Br2

[NEt4](2)[Tc(Cl)(3)(CO)(3)] was prepared directly from [NBu4][TcO4]. Dissolution of [NEt4](2)[Tc(Cl)(3)(CO)(3)] in water yielded the aqua ion [Tc(OH2)(3)(CO)(3)](+) which, upon titration with 1 eq. of OH-, gave the tetranuclear complex [{Tc(mu(3)-OH)(CO)(3)}(4)] in quantitative yield and of which the structure could be elucidated. Reaction of [{Tc(mu(3)-OH)(CO)(3)}(4)] with HC5Me5 gave the important starting material [(C5Me5)M(CO)(3)] (M = Tc, Re). To achieve complexes in higher oxidation states with the C5Me5- ligand, oxidation was performed with [Br-2] for the rhenium and the corresponding technetium complex. Oxidation in trifluoroacetic acid yielded cis/trans-[(C5Me5)M(Br)(2)(CO)(2)] (M = Tc, Re). Oxidation in dichloromethane gave in both cases the seven co-ordinate, 18e(-) M(III) complex [(C5Me5)MBr(CO)(3)](+). The structure of the rhenium complex was elucidated. It was found that oxidation took place at the metal centre and the C5Me5- ring to yield [(CO)(3)M(mu-Br)(3)M(CO)(3)] as the counterion. (C) 1998 Elsevier Science Ltd. All rights reserved.